In an uplink from a user equipment to a radio base station, the transmission powers of different uplink channels usually are set relative to a reference channel, for example in Wideband Code Division Multiple Access (WCDMA) the Dedicated Physical Control Channel (DPCCH). The power difference relative to the reference channel is called power offset.
Suppose the power needed for the data channel is Powerdata in the decibel scale, and the power of the reference control channel is Powerrefe in the decibel scale, the relationship between them may be expressed as:Powerdata=Powerrefe+Δdata  (1)
In the above function, Δdata is the power offset relative to the power of the reference channel.
Depending on the amount of data to be transmitted on the data channel, the transport format is different, which specifies the parameters used in transmission, for example, the modulation type, the spreading factor, the number of channelization codes and the channel coding rate. For different transport format, to get the desired transmission error performance, for example, Block Error Rate (BLER), the required power is different. Therefore, the power offset depends on the transport format used on the data channel. And usually there is a table to describe the relationship between the transport format and the required power offset.
The Node B and the UE both need to know this table for scheduling and transport format selection and etc. Currently, the table is signalled to the UE. When the number of transport formats is large, signalling the whole table requires large signalling overhead. Therefore, usually, only several transport formats are selected as reference transport formats, and their power offsets are signalled to the UE. For other non-reference transport formats, their power offsets need to be calculated by interpolation based on the signalled power offsets of the reference transport formats, for example, in Enhanced Uplink. The power offsets of these reference transport formats are obtained by link-level simulation.
There are some problems for the current solution, however. Firstly, signalling overhead is needed. Secondly, even only signalling reference values which may save some signalling overhead, it is hard to ensure the accuracy of the power offset values for the below reasons:                The power offset obtained by link-level simulation may not accurate, where only a typical set of simulation parameters is assumed. (For example TU3 or RA50);        The interpolation to calculate the non-reference power offset values may introduce errors;        In order to save signalling overhead, the signalled power offset values need to be quantized, which may introduce quantization errors.        